I cook several butts at one time and keep it in the freezer. I do the same with brisket and chicken thighs. The best way I've found is to tightly wrap chunks in saran wrap, of the size I will want to thaw out for a meal, then put all of the individually wrapped portions in a zip lock freezer bag, pressing as much air out as possible. When I reheat it, it is close to being as good as when it came off the smoker.